1. Field of the Invention
The present invention relates to radio frequency communications and, more specifically, to an antenna system employed in radio frequency communications.
2. Description of the Prior Art
Radio signals usually start with electrical signals that have been modulated onto a radio frequency carrier wave. The resulting radio signal is transmitted using an antenna. The antenna is a resonant system that generates an electrical field (E field) and a magnetic field (H field) that vary in correspondence with the radio signal, thereby forming radio frequency radiation. At a distance from the antenna, as a result of transmission effects of the medium through which the radio frequency radiation is being transmitted, the E field and the H field fall into phase with each other, thereby generating a Poynting vector, which is given by S=Exc3x97H, where S is the Poynting vector, E is the E field vector and H is the H field vector.
Most conventional antenna systems are resonant systems that take the form of wire dipoles that run electrically in parallel to the output circuitry of radio frequency transmitters and receivers. Such antenna systems require that the length of the wires of the dipoles be at least one fourth of the wavelength of the radiation being transmitted or received. For example, if the wavelength of the radiation is 1000 ft., the length of the wire must be 250 ft. Thus, the typical wire antenna requires a substantial amount of space as a function of the wavelength being transmitted and received.
A crossed field antenna, as disclosed in U.S. Pat. No. 6,025,813, employs two separate sections which independently develop the E and H fields and are configured to allow combining the E and H fields to generate radio frequency radiation. The result is that the antenna is not a resonant structure, thus a single structure may be used over a wide frequency range. The crossed field antenna is small, relative to wavelength (typically 1% to 3% of wavelength) and provides high efficiency. The crossed field antenna has the disadvantage of requiring a complicated physical structure to develop the E and H fields in separate sections of the antenna.
Therefore, there is a need for a simple and compact antenna.
The disadvantages of the prior art are overcome by the present invention which, in one aspect, is an antenna system for transmitting and receiving, in association with a radio device, electromagnetic radiation having an E-field component and an H-field component. The electromagnetic radiation corresponds to a radio frequency power signal having a current and a voltage at a radio frequency. The antenna system includes a first radiating element and a second radiating element, each comprising a conductive material. The second radiating element is spaced apart from, and in alignment with, the first radiating element. A phasing and matching network is in electrical communication with the first radiating element, the second radiating element and the radio device. The phasing and matching network aligns the relative phase between the current and the voltage of the radio frequency power signal so that the H-field component of the corresponding electromagnetic signal is nominally in time phase with the E-field component.
In another aspect, the invention is a method of transmitting and receiving, in association with a radio device, electromagnetic radiation having an E-field component and an H-field component, wherein the electromagnetic radiation corresponds to a radio frequency power signal having a current and a voltage at a radio frequency. In the method, the relative phase between the current and the voltage of the radio frequency power signal is aligned so that the H-field component of the corresponding electromagnetic signal is nominally in time phase with the E-field component.
These and other aspects of the invention will become apparent from the following description of the preferred embodiments taken in conjunction with the following drawings. As would be obvious to one skilled in the art, many variations and modifications of the invention may be effected without departing from the spirit and scope of the novel concepts of the disclosure.